The present invention relates to apparatus and methods for joining adjacent ends of turbine rotor shafts and particularly relates to couplings between axially aligned steam turbine rotor shafts in a manner to reduce bearing-to-bearing span, increase rotor stiffness and enable additional rotor staging or rotor length reduction.
In turbines, particularly steam turbine rotor trains, it is frequently necessary to couple rotor shafts in axial alignment with one another within a given steam path due to material property limitations in the rotor shafts. The coupling requires axial space which adds span to the bearing-to-bearing length. In typical axial couplings for aligned rotor shafts, the axially adjoining rotor shaft ends have flanges with aligned bolt holes enabling the flanges to be bolted directly to one another. It will be appreciated therefore that the shaft end portions mounting the flanges require considerable additional axial extent to accommodate their coupling. This in turn leads to increases in overall span length between bearings with undesirably reduced rotor stiffness. Consequently, it has been found desirable to couple adjoining rotor shaft end portions to one another in a manner with reduced bearing-to-bearing span, thus stiffening the rotor, and enabling tighter clearances and additional turbine staging or rotor length reduction.